Fuel injection systems for internal combustion engines typically fall into one of two general categories. One type of fuel injection system is a "throttle body" system wherein one or more fuel injectors combine fuel with the flow of air entering a throttle valve connected to the engine intake manifold. The fuel is atomized and intermixed with the air flow in the course of movement through the throttle valve and intake manifold. The intake manifold distributes the air-fuel mixture into the inlet ports of each engine combustion chamber.
Another category of fuel injection systems is the "port system" in which a separate fuel injector is provided for each cylinder of the internal combustion engine. These fuel injectors are mounted on a fuel rail carried by the intake manifold from which they receive a supply of fuel. Each injector is effective to transmit a precisely metered quantity of atomized fuel directly into the inlet port of one of the cylinders of the engine.
Throttle body fuel injection systems and port fuel injection systems of the type described above each have advantages and disadvantages, which, to at least some extent, limits their efficiency and/or practicality in some applications. Throttle body fuel injection systems have the advantage of lower cost because only a limited number of fuel injectors are required to intermix the fuel with the flow of air entering the throttle valve of the engine. The problem with such systems is that engine performance can suffer as a result of incomplete fuel atomization, uneven intermixture of air and fuel, and/or improper distribution of the air-fuel mixture to each of the individual cylinders of the engine. Some of these problems are overcome by port fuel injection systems because each cylinder of the engine is provided with its own fuel injector. Nevertheless, the fuel rails and large number of injectors required in port fuel injection systems are costly compared to throttle body fuel injection systems.
The advantages and disadvantages of the fuel injection systems described above has prompted the development of alternative systems, such as those disclosed in U.S. Pat. No. 5,082,184 to Stettner et al. and U.S. Pat. No. 4,570,598 to Samson et al. In fuel injection systems of this type, a single injector is employed to distribute accurately metered quantities of fuel into each of a number of tubes leading to the respective cylinders of the internal combustion engine. These systems eliminate the need for separate electronic fuel injectors for each cylinder as in port fuel injection sytems, but more accurately and effectively intermix and distribute the air-fuel mixture to the engine cylinders compared to throttle body injection systems. The single point fuel injection system disclosed in the U.S. Pat. No. 4,570,598 to Samson et al., for example, includes an injector housing formed with a fuel collection chamber within which a ball valve is movable with respect to the inlets of a number of fuel orifices formed in an injector tip. Each of the fuel orifices has an outlet which is oriented in alignment with a respective fuel distribution passage formed in the injector housing. Each fuel distribution passage, in turn, is connected by a separate line to one of the cylinders of an internal combustion engine. Fuel is introduced into each of the fuel orifices when the ball valve is opened, and then a separate stream of fuel is ejected from each orifice into an air chamber at the base of the injector housing toward one of the fuel distribution passages. In the course of movement through the air chamber, the fuel is intermixed with the air so that an air-fuel mixture enters a respective fuel distribution passage for supply to the cylinders of the engine.
Air-assist single point injector systems such as that disclosed in U.S. Pat. No. 4,570,598 suffer from a number of limitations. Because the fuel orifices in the injector tip are physically spaced across an air chamber from the fuel distribution passages in the injector housing, dirt and debris in the fuel or within the air entering the air chamber can collect within the fuel orifices and fuel distribution passages. This can clog the fuel orifices or at least cause a sufficient obstruction so that the fuel cannot be smoothly directed from the fuel orifices into the fuel distribution passages. Further, in addition to problems of clogging, the heat from the engine can cause fuel to varnish or coke within the interior of the fuel injector. If such deposits accumulate at the discharge end of the fuel orifices, the stream of fuel emitted therefrom may be completely blocked or misdirected to such an extent that it contacts a wall of the injector housing rather than entering a fuel distribution passage.
In addition to the problems noted above, single point metering systems of the type disclosed in U.S. Pat. No. 4,570,598 may not effectively atomize and intermix the fuel and air before it is supplied to the cylinders of the engine. It is believed that whatever atomization of the fuel which does take place in systems of this type occurs within the lines leading from the injector housing to each cylinder. Little or no atomization could occur within the air chamber across which the fuel is transmitted from the fuel orifices to the fuel distribution passageways, because a plume or spray of air and fuel would form which would prevent at least a portion of the fuel from entering the fuel distribution passages. Consequently, atomization of the fuel and intermixture of the atomized fuel with air is not as complete as desired, and can therefore result in loss of engine performance and increased hydrocarbon emissions.
A still further limitation of the single point metering system disclosed in U.S. Pat. No. 4,570,598 is that it cannot be utilized with forced induction systems such as turbochargers and superchargers. In such system, pressurized air is introduced from a turbocharger or supercharger for intermixture with the fuel. But the air chamber of U.S. Pat. No. 4,570,598 is designed to receive only ambient pressure air and is provided with a vent which would prevent pressurization of the air chamber above ambient. As such, turbochargers or superchargers would not be effective in enhancing engine performance with the single point metering system described in U.S. Pat. No. 4,570,598.